Olefins containing fluorine compounds play an important role as refrigerant. In recent years, one of olefin containing compound namely 2,3,3,3-tetrafluoropropene (HFO-1234yf) has attracted attention as a new refrigerant to replace another fluorinated refrigerant namely 1,1,1,2-tetrafluoroethane (HFC-134a) which is a greenhouse gas.
The JP Application No. 40-2132 describes a process for the preparation of olefins containing fluorine by heating a mixture of methyl chloride and chlorodifluoromethane in the mol ratio of 5:1 at the temperature range of 600° C. to 1000° C. in the presence of steam.
The U.S. Pat. No. 2,931,840 describes a process for the preparation of HFO-1234yf by heating and decomposing a mixture of methyl chloride and chlorodifluoromethane or tetrafluoroethylene at a temperature of from 700 to 950° C. by a common heating means such as an electric heater in a reactor.
The U.S. Pat. No. 9,206,096 describes a process for the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf) from chlorodifluoromethane (R22) and methyl chloride (R40), such amounts that the R40 would be in a ratio of from 0.01 to 3 mol to 1 mol of the R22. One of the byproduct formed in the reaction is chloro trifluoroethylene (CTFE). The boiling point of CTFE is −28° C. which is very close to the boiling point (−29° C.) of 2,3,3,3-tetrafluoropropene and thus, it becomes a challenge to separate or purify 2,3,3,3-tetrafluoropropene by routine separation and/or purification techniques, such as distillation.
In the present invention, by using a higher molar ratio, we have found that CTFE formed in comparison to 2,3,3,3-tetrafluoropropene can be substantially reduced and it is possible to obtain 2,3,3,3-tetrafluoropropene having a higher purity.
U.S. Pat. No. 8,252,964 describes a process for purification of 2,3,3,3-tetrafluoropropene containing saturated halogenated impurities using molecular sieves of size 5 Å to 11 Å. The saturated halogenated impurities mentioned are 236ea, 245eb, R254. Such impurities are bulky in nature and therefore requires molecular sieves of size greater than 7.5 Å.
U.S. application Ser. No. 12/308,327 describes a process of drying a fluid comprising a 2,3,3,3-tetrafluoropropene and water using molecular sieve of size 3 Å to 5 Å. PCT Publication No. 2015/053339 describes a process for purification of 2,3,3,3-tetrafluoropropene by distillation of composition 2,3,3,3-tetrafluoropropene and the methyl chloride and the fluorinated compounds having a boiling point of −14 to −30° C. Such composition upon distillation forms azeotropic composition and the azeotrope like composition of 2,3,3,3-tetrafluoropropene and the methyl chloride. U.S Patent Application No. 2015/0291490 describes a process for separation of 2,3,3,3-tetrafluoropropene and methyl chloride from azeotrope or azeotrope-like composition of 2,3,3,3-tetrafluoropropene and methyl chloride by contacting such composition with specific extraction solvent. An azeotrope composition of 2,3,3,3-tetrafluoropropene and methyl chloride is defined as a composition wherein the content ratio of 2,3,3,3-tetrafluoropropene and methyl chloride is mol % ratio of 63 mol % and 37 mol % respectively. An azeotrope-like composition is a composition wherein the content ratio of 2,3,3,3-tetrafluoropropene is 58 to 78 mol % and content ratio of methyl chloride is 22 to 42 mol %.
In view of the above, there is an urgent need to develop an industrially advantageous, efficient process for preparing 2,3,3,3-tetrafluoropropene.
The present inventors have surprisingly observed upon treatment of an anhydrous mixture comprising 2,3,3,3-tetrafluoropropene and methyl chloride, with molecular sieves of size 3 Å to 5 Å resulted in the selective adsorption of methyl chloride. Thus, aiding in the purification of 2,3,3,3-tetrafluoropropene. It has also been observed that the process of 2,3,3,3-tetrafluoropropene become industrially viable when methyl chloride and chlorodifluoromethane has been taken in molar ratio 3.2 to 4.7.